It is well known that surface coatings (e.g., water-based or solvent-based paints, stains, varnishes, anti-graffiti coatings, and the like) are susceptible to attack by microorganisms. Such attack may occur in the wet state (i.e., commonly referred to as “in-can” spoilage) or it may occur on the surface of the surface coating after application to a substrate.
Surface coatings typically contain a number of ingredients that may be susceptible to in-can spoilage by the action of microorganisms. Examples include binder, thickener, and other ingredients such as coalescing agents and defoamers. Water-borne (e.g., latex) paints and coatings are particularly prone to in-can spoilage by microorganisms. Examples of organisms that may cause in-can spoilage include Alcaligenes species, Bacillus species, E. coli, Micorococcus luteus, Proteus vulgaricus, Pseudomonas species, Candida albicans, Saccharomyces cerevisiase, Aspergillus species and Penecillium species. In-can spoilage may be characterized, for example, by gassing, discoloration, reduced viscosity, ropiness, and phase separation.
After a surface coating composition has been applied to a surface to form a coating, organisms in the environment (e.g., fungi or algae) may begin to grow on the surface of the film if conditions are favorable (e.g., the presence of moisture and humidity). The presence of organisms on the film is undesirable and may result in film degradation, for example, discoloration, dulling, loss of integrity, increased dirt retention, and loss of adhesion of the film. Examples of species that may grow on the dried films include Aspergillus sp., Penecillium sp., Cladosporium sp., Aurebasidium sp., Alternaria sp., Mucor sp., and Trichoderma. Yeasts (e.g., Candida and Rhodotorula) are also found in areas with high humidity, for example, bathrooms.
Mold growth on dried films not only results in the discoloration and disfigurement, but also may contribute to air quality and health issues for the building inhabitants. Surface growth may contribute to “sick-building syndrome” by contributing to the spore load in the air. It is now recognized that fungal spores and bacteria may be allergens and may cause health problems (Reiss, 1986). Some of the symptoms include respiratory problems, skin rashes, heart palpitations, headaches, and chronic fatigue.
In order to provide overall protection, surface coating compositions may comprise two or more preservatives including: (1) an “in-can” preservative for wet-state protection of the surface coating; and (2) a dry film preservative for protection of the dried surface coating.
Desirable properties of the in-can preservative include a broad-spectrum activity, low toxicity, cost effectiveness, quick kill rate, minimal discoloration, low odor, and low partition coefficient. The requirements for the dry film preservative are similar to those for an in-can preservative, except that dry film preservatives are desirably longer-lasting and more effective against fungi than in-can preservatives.
In view of the foregoing, surface coating compositions comprising preservatives that have low toxicity, broad spectrum efficacy including both in-can and dry film efficacy, quick kill rate, minimal discoloration, and low odor are highly desirable.